This is American planners' worst fear. City combat blunts the U.S. military advantages of speed and knowledge. What the Pentagon calls "urban canyons" offers hideouts for foes and civilians as well as sniper nests and underground lairs from which combatants can strike. Buildings create vast "dead spaces" for an enemy to exploit out of the sight of those trying to kill Saddam. They hinder communication and hamper anything flying low, like helicopters, spy drones and warplanes assisting forces on the ground. In cities, mobility and maneuver—two tenets of U.S. ground-combat strategy—hit a dead end.

Commanders in urban environments can't survey the entire battlefield and instead see only bits and pieces; it's like playing chess while viewing only four squares on the board. This battlefield compression means that low-ranking corporals and sergeants—not colonels and captains—must often make life-and-death decisions. These choices come fast and furious when you're fighting downtown: 90% of the targets are less than 50 yards away and seen for only seconds. Killing innocent civilians—or your own men—is a risk that goes with the terrain. A quarter of all explosive rounds turn into duds when they glance off walls and roofs. Helicopters can get tangled in overhead wires and crash. And America's most promising gizmos—robots that can crawl from building to building, miniature drones that can spy around corners, acoustic sensors capable of taking out snipers—are still unproven. The hottest "new" technology at last month's war game: John Deere two-seat Gator tractors, which can zip through narrow passageways bringing ammo and supplies to the front and returning with casualties.

Undeterred, Pentagon planners are poring over maps and plotting potential invasion routes along Baghdad's streets and even through its sewers. The sprawling capital is marked by broad boulevards, labyrinthine alleys and 5 million people. Missile batteries surround the city, along with most of the 15,000-man élite Special Republican Guard. "If they come, we are ready," Saddam told a British newspaper last month, reportedly from a bunker beneath Baghdad. "We will fight them on the streets, from the rooftops, from house to house."

Saddam's rhetoric is probably overblown. Iraqi soldiers may well surrender as readily as they did in 1991 after 38 days of heavy bombing. But the Iraqi leader, intelligence officials believe, is shrewdly calculating that the U.S. military brass—and the American public—cannot stomach the prospect of sizable losses in such an exchange. Think back to the debacle in Mogadishu, Somalia, in 1993 (chronicled in the movie Black Hawk Down), when 18 U.S. troops were killed, prompting a quick American withdrawal from that African nation. In Iraq there is the added risk that Saddam will use biological or chemical weapons against American troops. U.S. military leaders say 30% of street-fighting combatants tend to end up as casualties. The Pentagon wants to drive that figure down to 10%.

Any invasion of Baghdad would most likely start under cover of darkness. U.S. troops, brought in by helicopters, would seek a secure foothold from which to expand their presence in the city. The biggest advantage U.S. troops would have in downtown Baghdad would be their night-vision devices, giving them a greenish but clear-eyed view of a nighttime world. Once inside Baghdad, the Americans would start clearing buildings one by one, from the top floor down. They would probably use the technique that Israeli forces employed during fighting earlier this year in the West Bank's Balata refugee camp. Once inside a building, Israeli forces moved to the next one by cutting holes in the adjoining walls. That kept the Israeli troops largely inside and safe from Palestinian sniper fire. The U.S. has a wide range of wall-breaching weapons, ranging from M-1 tanks to exploding tape to crowbars. Traveling through walls, though time-consuming, also helps troops elude the booby traps that are often rigged to doors and windows.

There is also an entirely different tactic the U.S. could adopt in taking on Baghdad. Robert Scales, a retired major general who used to run the U.S. Army War College, says the Americans should avoid door-to-door battles and instead cordon off the capital with a loose chain of tanks and armored vehicles. This porous ring would allow civilians to flee the city center, where Saddam's soldiers—and perhaps the Iraqi leader himself—would be holed up, anxiously waiting for a "mother of all battles" that would never materialize. "You can be patient, with a minimum loss of life," says Scales, "or you can rush in and kill a lot of people on both sides."

Baghdad would seem particularly vulnerable to such a wait-it-out strategy. It is not even close to being self-sufficient. If U.S. troops cut off the supply of water, food, electricity and communications, civilians would no doubt quickly begin fleeing to the safety of refugee camps set up outside the cordon. The U.S. military could wait for the white flag of surrender to flutter outside the range of most of Saddam's weapons. Armed with intelligence gleaned from fleeing refugees, the Americans could attack key targets inside the city with long-range weapons. Such a siege could help nurture one prized U.S. goal: Saddam's falling at the hands of his own people. "Baghdad is one of those classic cities that happen to contain all the kindling necessary to spark a revolt," says Scales. "You'd have the ruling élite and the army cheek by jowl with the people, who despise both the élite and the army."

—With reporting by Matt Rees and Aharon Klein/Jerusalem

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